In lighting units with LEDs, e.g., additional brake lights for motor vehicles, the LEDs are usually mounted on a circuit board together with appropriate current limiting resistors. To protect the LEDs and optionally to improve the light distribution, a protective lens (a glass panel in the simplest case) is placed in front of it. German Pat. No. 196 35 564 describes that resistors may be designed as wired components, surface mount devices (SMD) or in the form of a resistance layer on the circuit board.
Japanese Pat. No. 5119706 describes a lighting unit where LED chips are mounted on a glass panel. To this end, the glass panel is coated on one side with a layer of indium-tin oxide (ITO) structured in a photolithographic process. First contact areas are applied in the form of a gold layer at the points where the LED chips are to be placed, and second contact areas also in the form of a gold layer are applied at adjacent locations, and the LED chips are attached to the first contact areas by die bonding with the help of electrically conducting adhesive and are bonded to the second contact areas by wire bonding. Due to the structure and mounting of the LED chips, they emit light in the direction away from the glass panel holding them.
Japanese Pat. No. 4199754 describes a similar lighting unit which differs from the conventional lighting unit described above in that a nickel-phosphorus layer is applied to the structured ITO layer and then a gold layer is applied to this, with the LED chips being attached to the gold layer over the first and second contact areas by die bonding and wire bonding. The nickel-phosphorus layer assumes the function of current limiting resistors for the individual LEDs. Here again, due to the structure and mounting of the LED chips, they emit light in the direction away from the glass panel holding them.
Surface mount (SMD) LEDs which, when assembled on a circuit board, have their light emitting side facing the circuit board, with the light passing through a hole in the circuit board, are described by Stanley Electric Sales of America, Inc. (online Internet address: URL: http://www.stanleyelec.com/smt/rm.htm (as of Nov. 17, 1998). Similar LEDs are also distributed by Siemens AG under the name "Hyper TOPLED.RTM. RG."